The present invention relates to a technology for chemical reactions through effective use of heat from a heat source, which is applicable to reactors to be produced by microfabrication, reformers based on said reactors, and power supply systems.
A fuel cell as a new power source is expected to find use for portable electronic machines and equipment because of its higher energy density and longer life compared with secondary batteries. There are several types of small-sized fuel cells, which consume hydrogen (stored in a hydrogen occluding material) as fuel or methanol solution as fuel, or which employ the direct methanol system so designed as to produce output through direct reaction in the cell. Recently, attempts are being made to develop the small-sized fuel cell of reforming type, which is constructed such that hydrocarbon fuel (such as methanol) passes through a reformer to yield hydrogen, which subsequently reacts with oxygen in the cell to generate electric energy.
Production of hydrogen with a high conversion efficiency has become possible owing to catalyzed chemical reactions in a chemical apparatus called “micro-reactor”, which is formed on a silicon wafer by the semiconductor process. This technique is suitable for small-sized reformers.
One example of such reformers is known as the tubular reactor of cantilever structure. (See patent document; International publication No. 03/013729, pamphlet.) This reactor has two separated U-shaped channels made of thin silicon nitride tube. The free ends of the channels form the reaction zones covered with silicon. Between the tubes are a number of silicon slabs (joining them together) for heat exchange.
The conventional apparatus, however, has the following problems involved in the device structure and the temperature distribution in the heat exchanger that connects the channels to each other.
The heat exchanger should provide uniform temperature distribution in the reactor for high heating efficiency. (It is necessary to avoid local temperature fluctuation.) This requirement leads to a heat exchanger in complex structure, which needs a number of parts and manufacturing steps. These factors prevent size reduction, thickness reduction, cost reduction, and efficiency improvement.
Moreover, uneven temperature distribution in the reactor tends to give rise to by-products, thereby decreasing reaction efficiency.
In addition, it is necessary that waste heat originating from fuel combustion should be effectively used to heat fuel for reforming; otherwise, considerable heat loss is accompanied by outflow (emission) of fluid, which lowers the efficiency of the apparatus.